Calculate frequency from MIDI note number and vice versa.
This lib comes with tests and instructive¹ source code. (¹ at least for future me, hopefully.)
from test.usage.js:
var mnf = require('midi-notefreq-pmb');
function testNote(noteName, expectMidiNote, expectFreqHz) {
var midiNote = mnf.sciUK2midiNote(noteName);
equal(midiNote, expectMidiNote);
equal(mnf.midiNote2sciUK(expectMidiNote), noteName);
equal(mnf.midiNote2freqHz(midiNote), expectFreqHz);
equal(mnf.freqHz2midiNote(expectFreqHz), expectMidiNote);
}
testNote('C-1', 0, 8.175798915643707);
testNote('C4', 60, 261.6255653005986);
testNote('A4', 69, 440.0);
testNote('A3', 57, 220.0);
testNote('A5', 81, 880.0);
testNote('G9', 127, 12543.853951415975);
equal(mnf.sciUK2midiNote(['C-1', 'C4', 'A4', 'A3', 'A5', 'G9']),
[ 0, 60, 69, 57, 81, 127 ]);
function testFreq(noteName, offset, freqHz) {
var expectMidiNote = mnf.sciUK2midiNote(noteName) + offset;
equal(mnf.freqHz2midiNote(freqHz), expectMidiNote);
floatAlmostEqual(mnf.midiNote2freqHz(expectMidiNote), freqHz);
}
testFreq('A3', 0, 220.0);
testFreq('A4', 0, 440.0);
testFreq('A4', 0.42748691676866, 451.0);
testFreq('F#9', 0.72430607743638, 12345.6789);- needs more/better tests and docs
ISC